The present invention relates to a geometric modeling system which constitutes a base for the construction of various automatic systems which automatically perform various works necessary in the design and production of goods with the aid of computers, such as systems known as CAE, CAD and CAM. More particularly, the invention is concerned with a geometric modeling system which is suitable for use in interactive operations.
In generating a three-dimensional form from two-dimensional wire frame patterns or figures which are typically produced by a drafting system, it is necessary that a three-dimensional surface be stored in a computer in such a mathematically complete form that the relationships of points, lines and surfaces are represented by a solid model in terms of boundary expression. To this end, it has been a common practice to employ a process which has the steps of cutting the wire frame which represents the boundary of the actual object out of the two-dimensional wire frame in accordance with the form of the object through an interactive method, appointing the cut wire frames sequentially so as to take up the surfaces or the boundaries of the surfaces which constitute the three-dimensional object, and synthesizing them so as to complete the three-dimensional form. This method is disclosed, for example, in pp 23-28, "COMPUTERS IN ENGINEERING 1982 Vol. 1" which was released in the Second International Computer Engineering Conference which was held in August, 1982.
The conventional graphic system, however, is not convenient for the users in that it requires a large number of command inputs in the interactive processing, as well as laborious inputting operations.
Another problem is that the two-dimensional wire frame pattern formed by the drafting system sometimes irregularly or incompletely indicate the states of intersection between the constituent lines such as straight lines and arcuate lines, so that the user cannot correctly recognize the states of intersection of the lines from the pattern on display. Therefore, the user must define again the data concerning such irregular and incomplete wire frame patterns, thereby to obtain regular and complete presentation, following laborious inputting steps.
It is to be pointed out also that the work for appointing the wire frames which represent the boundaries in the actual object and the work for visually recognizing the three-dimensional structure from the design drawings are not always conducted in concert with each other, with the result that the performance of the man-machine interface for inputting modeling commands is impeded seriously.